Threatened predators Why sharks off Brazil's coast are on cocaine

Normally people are caught with the drug. In Rio de Janeiro, sharks have tested positive for cocaine for the first time. Where does it come from and what consequences can it have for the animals?

In the Brazilian coastal metropolis of Rio de Janeiro, sharks have tested positive for cocaine. Researchers from the Oswaldo Cruz Institute detected the drug in the livers and muscles of 13 sharpnose sharks (Rhizoprionodon lalandii), as the study published in the journal "Science of The Total Environment" shows. The data would indicate the large quantities of the drug consumed in the city and disposed of in the sea via wastewater, it said.

"In Brazil, studies have already shown the contamination of water and some aquatic organisms, such as mussels, by cocaine. Our analysis is the first in which the substance has been found in sharks," says pharmacist Enrico Mendes Saggioro, one of the researchers responsible for the discovery together with biologist Rachel Ann Hauser-Davis.

According to the biologist, as predators, sharks play a central role in the food chain in the marine ecosystem - they can be used to detect environmental damage, including various forms of pollution.

Possible consequences for sharks

According to the latest World Drug Report, published by the United Nations Office on Drugs and Crime (UNODC) in 2024, Brazil is one of the largest consumers of cocaine in the world. According to the available studies, researchers assume that the drug enters the sea primarily through the disposal of cocaine waste in wastewater.

Specific studies are needed to determine the exact consequences of cocaine exposure for the animals. "It is suspected that it affects the growth, maturation and possibly the fertility of the sharks, as the liver is involved in the development of embryos," says biologist Hauser-Davis.

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